Picture this, for example: Doctors use a tiny sponge to soak up
a drug and deliver it directly to a tumor. Chemists at a
manufacturing plant use another to trap and store unwanted
gases.

These technologies are what UB faculty member Jason Benedict had
in mind when he led the design of a new material called UBMOF-1.
The material — a metal-organic framework, or
“MOF” — is a hole-filled crystal that could act
as a sponge, capturing molecules of specific sizes and shapes in
its pores.

Swiss cheese-like MOFs are not new, but Benedict’s has a
couple of remarkable qualities:

The crystal’s pores change shape when hit by
ultraviolet light. This is important because changing the pore
structure is one way to control which compounds can enter or exit
the pores. You could, for instance, soak up a chemical and then
alter the pore size to prevent it from escaping. Secure storage is
useful in applications like drug delivery, where “you
don’t want the chemicals to come out until they get where
they need to be,” Benedict says.

The crystal also changes color in response to ultraviolet
light, going from colorless to red. This suggests that the
material’s electronic properties are shifting, which could
affect the types of chemical compounds that are attracted into the
pores.

Benedict’s team reported on the creation of the UBMOF on
Jan. 22 in the journal Chemical
Communications. The paper’s co-authors include chemists
from UB and Penn State Hazleton.

“MOFs are like molecular sponges — they’re
crystals that have pores,” explains Benedict, assistant
professor in the Department of Chemistry.

“Typically, they are these passive materials:
They’re static. You synthesize them and that’s the end
of the road,” he adds. “What we’re trying to do
is to take these passive materials and make them active so that
when you apply a stimulus like light, you can make them change
their chemical properties, including the shape of their
pores.”

Benedict is a member of UB’s New York State Center of
Excellence in Materials Informatics, which the university launched
in 2012 to advance the study of new materials that could improve
life for future generations.

To force UBMOF-1 to respond to ultraviolet light, Benedict and
colleagues used some clever synthetic chemistry.

MOF crystals are made from two types of parts — metal
nodes and organic rods — and the researchers attached a
light-responsive chemical group called a diarylethene to the
organic component of their material.

Diarylethene is special because it houses a ring of atoms that
is normally open but shuts when exposed to ultraviolet light.

In the UBMOF, the diarylethene borders the crystal’s
pores, which means the pores change shape when the diarylethene
does.

The next step in the research is to determine how, exactly, the
structure of the holes is changing and to see if there’s a
way to get the holes to revert to their original shape.

Rods containing diarylethene can be forced back into the
“open” configuration with white light, but this tactic
only works when the rods are alone. Once they’re inserted
into the crystal, the diarylethene rings stay stubbornly closed in
the presence of white light.